Abstract
AbstractThe curve number method for estimating rainfall runoff has continually evolved since its creation in the mid-20th century. Because it is inherently an empirical model that is broadly applied to many hydrological applications, the rationales for its parameters have become removed from physical interpretation over its evolution. The ASCE EWRI CN-Hydrology Committee, i.e., some of the foremost experts on this methodology, often finds itself internally at odds regarding many aspects of CN-hydrology. Here, the committee has synthesized its member’s perspectives on the physical interpretations of one CN-method parameter, the initial abstraction (Ia). This note provides insights into how the Ia concept has evolved and offers some context into reasons behind its evolution. This note also synthesized different interpretations of Ia within the framework of different hydrological settings, applications, and spatial scales. Broadly speaking, the committee suggests that Ia might need to be interpreted on a case-by-case basis although this note places reasonable boundaries on Ia for most applications.